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United States Patent |
5,001,219
|
Chern
,   et al.
|
March 19, 1991
|
High modulus poly-p-phenylene terephthalamide fiber
Abstract
High modulus, high tenacity fibers of poly-p-phenylene terephthalamide
(PPD-T) are disclosed along with a fiber heat treating process for
increasing the inherent viscosity and the crystallinity index of the
PPD-T. Never-dried fibers swollen with water of controlled acidity are
heated beyond dryness.
Inventors:
|
Chern; Terry S. (Richmond, VA);
De La Veaux; Stephan C. (Wilmington, DE);
Lahijani; Jacob (Wilmington, DE);
Van Trump; James E. (Hockessin, DE)
|
Assignee:
|
E. I. du Pont de Nemours and Company (Wilmington, DE)
|
Appl. No.:
|
300771 |
Filed:
|
January 23, 1989 |
Current U.S. Class: |
528/348; 528/183; 528/337; 528/344 |
Intern'l Class: |
C08G 069/46 |
Field of Search: |
528/348,183,337,344
|
References Cited
U.S. Patent Documents
3063966 | Nov., 1962 | Kwolek | 260/78.
|
3673143 | Jun., 1972 | Bair et al. | 260/30.
|
3817941 | Jun., 1974 | Bair et al. | 260/78.
|
3862897 | Jan., 1975 | Gattus et al. | 264/216.
|
3869429 | Mar., 1975 | Blades | 260/78.
|
3869430 | Mar., 1987 | Blades | 260/78.
|
4346215 | Aug., 1982 | Garlington et al. | 528/348.
|
4374977 | Feb., 1983 | Fujiwara et al. | 528/348.
|
4374978 | Feb., 1983 | Fujiwara et al. | 528/348.
|
4507467 | Mar., 1985 | Shimada et al. | 528/348.
|
4539393 | Sep., 1985 | Tamuro et al. | 528/348.
|
4560743 | Dec., 1985 | Fujiwara et al. | 528/348.
|
Foreign Patent Documents |
55-11763 | Mar., 1980 | JP.
| |
55-11764 | Mar., 1980 | JP.
| |
59-192713 | Nov., 1984 | JP.
| |
2044668 | Mar., 1980 | GB.
| |
2044669 | Mar., 1980 | GB.
| |
Other References
Journal of East China Institute of Textile Science and Technology, vol. 10,
No. 2, 1984, pp. 30-34.
Journal of East China Institute of Textile Science and Technology, vol. 10,
No. 2 (1984), pp. 30-34.
|
Primary Examiner: Anderson; Harold D.
Parent Case Text
This is a division of application Ser. No. 041,589, filed Apr. 27, 1987,
now U.S. Pat. No. 4,883,634, which was a continuation-in-part of
application Ser. No. 868,667, filed May 30, 1986, now abandoned.
Claims
What is claimed:
1. A fiber of poly-p-phenylene terephthalamide having a modulus of greater
than 1100 grams per denier, a tenacity of greater than 18 grams per
denier, an elongation of less than 2.0%, a moisture regain of less than
1.5%, an inherent viscosity of 5.5 to 20, and a Crystallinity Index of
70-85%, wherein inherent viscosity (IV) is defined by the equation:
IV=1n(.eta..sub.rel)/c
where c is the concentration (0.5 gram of polymer in 100 ml of solvent) of
a solution of poly-p-phenylene terephthalamide in 96% sulfuric acid as a
solvent and .eta..sub.rel is the ratio between flow times of the solution
and the solvent as measured as 30.degree. C. in a capillary viscometer and
wherein Crystallinity Index is defined as the ratio of the difference
between intensity values of the X-ray peak of a diffraction pattern of
poly-p-phenylene terephthalamide at 23.degree. and the minimum of the
valley at 22.degree. to the X-ray peak intensity of a diffraction pattern
of poly-p-phenylene terephthamide at 23.degree., expressed as percent.
2. A fiber of poly-p-phenylene terephthalamide having a modulus of greater
than 1100 grams per denier, and a tenacity of greater than 18 grams per
denier, an elongation of less than 2.0%, a moisture regain of less than
1.5%, and a Crystallinity Index of 75-85%, the polymer of said fiber
having an inherent viscosity of 6.5 to 20, wherein inherent viscosity (IV)
is defined by the equation:
IV=1n(.eta..sub.rel)/c
where c is the concentration of (0.5 gram of polymer in 100 ml of solvent)
of a solution of poly-p-phenylene terephthalamide in 96% sulfuric acid as
a solvent and .eta..sub.rel is the ratio between flow times of the
solution and the solvent as measured at 30.degree. C. in a capillary
viscometer and wherein Crystallinity Index is defined as the ratio of the
difference between intensity values of the X-ray peak of a diffraction
pattern of poly-p-phenylene terephthalamide at 23.degree. and the minimum
of the valley at 22.degree. to the X-ray peak intensity of a diffraction
pattern of poly-p-phenylene terephthamide at 23.degree., expressed as
percent.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Poly-p-phenylene terephthalamide fibers, long known for their light weight,
high strength, and high modulus, have found wide acceptance in a great
number of applications requiring their unique combination of properties.
The wide acceptance has, however, given rise to a demand and need for
fibers having still higher strength and modulus for use in still more
demanding applications. Fibers having decreased solubility and chemical
reactivity and increased overall crystallinity and resistance to moisture
regain have been sought and are in demand.
2Description of the Prior Art
U.S. Pat. No. 3,869,430, issued Mar. 4, 1975 on the application of H.
Blades, discloses fibers of poly-p-phenylene terephthalamide and processes
for making the polymer and the fibers. That patent is particularly
concerned with a process for heat treating such fibers after the fibers
have been dried. That patent discloses, generally, that fibers could be
heat treated whether wet or dry; but, in the examples, teaches heat
treatment only of dried fibers and, elsewhere in the specification,
cautions against heat treating fibers at excessive heat for excessive time
with the warning that decreased tenacity and decreased polymer inherent
viscosity will result.
Japanese Patent Publications No. 55-11763 and 55-11764 published Mar. 27,
1980, discIose fibers of poly-p-phenylene terephthalamide having high
modulus and high tenacity but with polymer exhibiting only moderate
inherent viscosity. The processes of those publications are particularly
concerned with a fiber-drawing step performed after coagulating the spun
polymer and before drying the fibers. In the drawing step, the fibers are
actually stretched to 20 to 80 or 90% of the maximum stretch attainable
before break. After the stretching, the fibers are dried at various times
and at temperatures above about 300 degrees and as high as 600 degrees for
three seconds. The inherent viscosity of the polymer of fibers so-made is
always disclosed to be less than the inherent viscosity of the starting
polymer and there is no suggestion that the inherent viscosity might be
increased by any heat treatment.
The Journal of East China Institute of Textile Science and Technology, Vol.
10, No. 2 (1984), pp. 30-34, discloses heat treatment of fibers under very
slight tension. There is teaching that the treatment causes decomposition,
branching, and cross-association with accompanying increases in molecular
weight. Neither fiber modulus nor degree of crystallinity is mentioned.
SUMMARY OF THE INVENTION
A process is provided by this invention for manufacturing a
poly-p-phenylene terephthalamide fiber having high modulus and high
tenacity wherein a wet, water-swollen, fiber is exposed to a heated
atmosphere, and the fiber, during exposure, is subjected to a tension. The
swollen fibers, preferably, have about 20 to 100 percent water, based on
dried fiber material, and the atmosphere is usually heated at 500 to 660
degrees with exposure of the fiber for 0.25 to 12 seconds. The tension on
the fibers is about 1.5 to 4 grams per denier (gpd). There is, also,
provision for controlling the acidity or basicity of the water-swollen
(never-dried) fibers to affect change in the inherent viscosity and
tenacity of the polymer during the heat treatment. Inherent viscosity of
the polymer after the heat treatment is high; more than 5.5 and as much as
20 or more; and is increased in the heat treatment. In order to maintain
satisfactory process operability and product properties, the basicity is
maintained at less than about 10 and the acidity is maintained at less
than about 60. Basicity of less than about 2 and acidity of less than
about 1.0 are preferred. Crystallinity Index of the heat treated polymer
is high; at least 70% and as. much as 85%.
In one embodiment of the invention, an entrainment jet is used for
application of hot gas to dry and treat the swollen fibers in an efficient
and effective manner. The process is very fast and, as a result, the
product of the jet embodiment of the process is a fiber having a
Crystallinity Index of greater than 75%. For use of the jet embodiment, it
is preferred that the swollen fiber should be exposed to a heated
atmosphere at 500 to 660 centigrade degrees for about 0.25 to 3 seconds,
and most preferably about 0.5 to 2 seconds. In the most preferable range,
there is some
allowance made for different sizes of yarns--the range is most preferably
0.5 to 1 second for 400 denier yarns and 0.5 to 2 seconds for 1200 denier
yarns.
In another embodiment of the invention, an oven is used for application of
radiant heat to cause slower drying of the swollen fibers; and, as a
result, the product of the oven embodiment is a fiber having an inherent
viscosity of more than about 6.5. For use of the oven embodiment, it is
preferred that the swollen fiber should be exposed to a heated atmosphere
at 500 to 660 degrees for about 3 to 12 seconds, and most preferably at
550 to 660 degrees for about 5 to 12 seconds, with less time required for
low denier yarn at a given temperature. For purposes of this invention,
radiant heating of the oven embodiment means that at least 75 percent of
the heat energy absorbed by the water-swollen yarn is radiant heat energy.
In the other embodiments, there can be combinations of the above heat
treatment embodiments which yield high modulus, high tenacity fibers with,
both, an increased inherent viscosity and an increased Crystallinity
Index.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is based on a treatment of poly-p-phenylene
terephthalamide fibers which, quite unexpectedly, gives rise to fibers of
high modulus and Crystallinity Index while permitting controlled increase
of the ultimate inherent viscosity. The invention permits manufacture of
high modulus fibers of poly-p-phenylene terephthalamide, having inherent
viscosity of greater than 6.5 and Crystallinity Index of greater than
about 75%.
By "poly-p-phenylene terephthalamide" is meant the homopolymer resulting
from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl
chloride and, also, copolymers resulting from incorporation of small
amounts of other aromatic diamine with the p-phenylene diamine and of
small amounts of other aromatic diacid chloride with the terephthaloyl
chloride. Examples of acceptable other aromatic diamines include
m-phenylene diamine, 4,4'-diphenyldiamine, 3,3'-diphenyldiamine,
3,4'-diphenyldiamine, 4,4'-oxydiphenyldiamine, 3,3'-oxydiphenyldiamine,
3,4'-oxydiphenyldiamine, 4,4'-sulfonyldiphenyldiamine,
3,3'-sulfonyldiphenyldiamine, 3,4'-sulfonyldiphenyldiamine, and the like.
Examples of acceptable other aromatic diacid chlorides include
2,6-naphthalenedicarboxylic acid chloride, isophthaloyl chloride,
4,4'-oxydibenzoyl chloride, 3,3'-oxydibenzoyl chloride, 3,4'-oxydibenzoyl
chloride, 4,4'-sulfonyldibenzoyl chloride, 3,3'-sulfonyldibenzoyl
chloride, 3,4'-sulfonyldibenzoyl chloride, 4,4'-dibenzoyl chloride,
3,3'-dibenzoyl chloride, 3,4'-dibenzoyl chloride, and the like. As a
general rule, other aromatic diamines and other aromatic diacid chlorides
can be used in amounts up to as much as about 10 mole percent of the
p-phenylene diamine or the terephthaloyl chloride, or perhaps slightly
higher, provided only the other diamines and diacid chlorides have no
reactive groups which interfere with the polymerization reaction.
Poly-p-phenylene terephthalamide fibers which include such small amounts
of other diacids or diamines and which are heat treated by this invention,
may exhibit physical properties slightly different from those which would
have been obtained had no other diacids or diamines been present.
The polymer can be conveniently made by any of the well known
polymerization processes such as those taught in U.S. Pat. No. 3,063,966
and U.S. Pat. No. 3,869,429. One process for making the polymer includes
dissolving one mole of p-phenylene diamine in a solvent system comprising
about one mole of calcium chloride and about 2.5 liters of
N-methyl-2-pyrrolidone and then adding one mole of terephthaloyl chloride
with agitation and cooling. The addition of the diacid chloride is usually
accomplished in two steps--the first addition step being about 25-35
weight percent of the total with the second addition step occurring after
the system has been stirred for about 15 minutes. Cooling is applied to
the system after the second addition step to maintain the temperature
below about 60.degree. C. Under forces of continued agitation, the polymer
gels and then crumbles; and, after a few hours or more, the resulting
crumb-like polymer is ground and washed several times in water and dried
in an oven at about 100.degree.-150.degree. C.
Molecular weight of the polymer is dependent upon a multitude of
conditions. For example, to obtain polymer of high molecular weight,
reactants and solvent should be free from impurity and the water content
of the total reaction system should be as low as possible --no more, and
preferably less, than 0.03 weight percent. Care should be exercised to
assure the use of equimolar amounts of the diamine and the diacid chloride
because only a slight imbalance in the reactant materials will result in a
polymer of low molecular weight While it may be preferred that inorganic
salts be added to the solvent to assist in maintaining a solution of the
polymer as it is formed, quaternary ammonium salts have, also, been found
to be effective in maintaining the polymer solution. Examples of useful
quaternary ammonium salts include methyl-tri-n-butyl ammonium chloride,
methyl-tri-n-propyl ammonium chloride, tetra-n-propyl ammonium chloride,
tetra-n-butyl ammonium chloride, and the like.
Fibers are made in accordance with the present invention by extruding a
dope of the polymer under certain conditions. The dope can be prepared by
dissolving an adequate amount of the polymer in an appropriate solvent.
Sulfuric acid, chlorosulfuric acid, fluorosulfuric acid and mixtures of
these acids can be identified as appropriate solvents. Sulfuric acid is
much the preferred solvent and must be used at a concentration of 98% or
greater to avoid undue degradation of the polymer. The polymer should be
dissolved in the dope in the amount of at least 30, preferably more than
40, grams of polymer per 100 milliliters of solvent. The densities of the
acid solvents are as follows H.sub.2 SO.sub.4, 1.83 g/ml; HSO.sub.3 Cl,
1.79 g/ml; and HSO.sub.3 F, 1.74 g/ml.
Before dissolving the polymer to make the spinning dope, the polymer should
be carefully dried to, preferably, less than one weight percent water; and
the polymer and the solvent should be combined under dry conditions. Dopes
should be mixed and held in the spinning process at as low a temperature
as is practical to keep them liquid in order to reduce degradation of the
polymer. Exposure of the dopes to temperatures of greater than 90.degree.
C. should be minimized
The dope, once prepared, can be used immediately or stored for future use.
If stored, the dope is preferably frozen and stored in solid form in an
inert atmosphere such as under a dry nitrogen blanket. If the dope is to
be used immediately, it can conveniently be made continuously and fed
directly to spinnerets. Continuous preparation and immediate use minimizes
degradation of the polymer in the spinning process.
The dopes are, typically, solid at room temperature and behave, in
spinning, like polymer melts. For example, a dope of 45 grams of the
polymer with an inherent viscosity of about 5.4 in 100 milliliters of 100%
sulfuric acid may exhibit a bulk viscosity of about 900 poises at
105.degree. C. and about 1000 poises at 80.degree. C., measured at a shear
rate of 20 sec.sup.-1, and would solidify to an opaque solid at about
70.degree. C. The bulk viscosity of dopes made with a particular polymer
increases with molecular weight of the polymer for given temperatures and
concentrations.
Dopes can generally be extruded at any temperature where they are
sufficiently fluid. Since the degree of degradation is dependent upon time
and temperature, temperatures below about 120.degree. C. are usually used
and temperatures below about 90.degree. C. are preferable. If higher
temperatures are required or desired for any reason, processing equipment
should be designed so that the dope is exposed to the higher temperatures
for a minimum time.
Dopes used to make the fibers of this invention are optically anisotropic,
that is microscopic regions of the dope are birefringent and a bulk sample
of the dope depolarizes plane-polarized light because the light
transmission properties of the microscopic regions of the dope vary with
direction. It is believed to be important that the dopes used in this
invention must be anisotropic, at least in part.
Fibers of the present invention can be made using the conditions
specifically set out in U.S. Pat. No. 3,869,429. Dopes are extruded
through spinnerets with orifices ranging from about 0.025 to 0.25 mm in
diameter, or perhaps slightly larger or smaller. The number, size, shape,
and configuration of the orifices are not critical. The extruded dope is
conducted into a coagulation bath through a noncoagulating fluid layer.
While in the fluid layer, the extruded dope is stretched from as little as
1 to as much as 15 times its initial length (spin stretch factor). The
fluid layer is generally air but can be any any other inert gas or even
liquid which is a noncoagulant for the dope The noncoagulating fluid layer
is generally from 0.1 to 10 centimeters in thickness.
The coagulation bath is aqueous and ranges from pure water, or brine, to as
much as 70% sulfuric acid. Bath temperatures can range from below freezing
to about 28.degree. C. or, perhaps, slightly higher. It is preferred that
the temperature of the coagulation bath be kept below about 10.degree. C.,
and more preferably, below 5.degree. C., to obtain fibers with the highest
initial strength
After the extruded dope has been conducted through the coagulation bath,
the dope has coagulated into a water-swollen fiber and is ready for drying
and heat treatment The fiber includes about 20 to 100% percent aqueous
coagulation medium, based on dry fiber material, and, for the purposes of
this invention, must be thoroughly washed to remove the proper amount of
salt and acid from the interior of the swollen fiber. It is now understood
that fiber-washing solutions can be pure water or they can be slightly
alkaline. Washing solutions should be such that the liquid in the interior
of the swollen fiber should have an acidity less than 60 and preferably
less than 10 and a basicity less than 10 and preferably less than 2
depending upon the conditions of the heat treatment and the desired final
inherent viscosity of the fiber product.
It is now believed that heat treatment of never-dried poly-p-phenylene
terephthalamide fibers results in alteration of the polymer in the fiber
in that the heat treatment causes a complex combination of polymerization,
depolymerization, branching and crosslinking reactions.
At temperatures from above 500.degree. C. to about 660.degree. C., at the
relatively short exposure times of this invention (0.25-12 sec), the
predominant reaction is believed to be branching and cross-linking which
lead to fibers with higher molecular weights and higher inherent
viscosities; these reactions are believed to be catalyzed by acids. Thus,
poly-p-phenylene terephthalamide never-dried fibers having an inherent
viscosity of about 5.5 and containing about 9 milliequivalents of acid or
less, showed little or no significant change in inherent viscosity when
heated at oven temperatures of 450.degree.-500.degree. C. for 6-9 seconds.
However, when heated at oven temperatures of 550.degree.-660.degree. C.,
these same never-dried fibers showed an unexpected and pronounced increase
in inherent viscosity up to or greater than 6.5, and the moduli increased
to about 1100 gpd or higher, while tenacities were maintained at 18 gpd or
higher. By contrast, when poly-p-phenylene terephthalamide fibers
containing about 150 milliequivalents of acid per kg of fiber were heated
in an oven even at temperatures as low as 410.degree. C. for 5 sec, the
inherent viscosities of the fibers were increased from about 5.5 to over
7, while fiber tenacity deteriorated from about 25 gpd to less than 16
gpd, below the range of interest of this invention.
Within the range of temperatures (500.degree.-660.degree. C.) and exposure
times (0.25-12 sec) of this invention, acidity of up to about 60 meq of
acid per kg of yarn is acceptable. Within that acidity limit, process
operability and product properties are acceptable. The upper limit of 60
acidity approximately corresponds to what is believed to be the sum of
acid groups attached to poly-p-phenylene terephthalamide polymer. The acid
groups are made up of carboxylic acid groups and sulfonic acid groups.
When a base such as sodium hydroxide is used in the fiber washing
processes, it is believed that the acid groups react with and neutralize
basic groups which are present in the fiber as a result of such washing
processes. Above about 60 meq of acid per kg of yarn, product quality and
processability deteriorate sharply.
The presence of small amounts of basic material, like sodium hydroxide, in
the never-dried poly-p-phenylene terephthalamide fibers prior to heating
under the conditions of time and temperature of this invention appear to
have little affect on those thermal reactions which yield high molecular
weights and inherent viscosities. Thus, when a series of poly-p-phenylene
terephthalamide fibers containing 1.5 milliequivalents of sodium hydroxide
per kg of fiber were heated in an oven at 550.degree.-640.degree. C. for
7-9 seconds, inherent viscosities were increased to from 7.0 to greater
than 20 and moduli to from 1060 to 1244, while tenacities were maintained
at greater than 18 gpd. At an oven temperature of 500.degree. C. for about
9 sec, poly-p-phenylene terephthalamide fibers containing this level of
base showed no change in inherent viscosity. At high levels of base in the
fibers, on the other hand, inherent viscosity was sharply reduced. Thus,
about 400 milliequivalents of sodium hydroxide in poly-p-phenylene
terephthalamide fibers, even at oven temperature as low as 410.degree. C.
for 5 sec, caused a dramatic drop in fiber properties to 3.0 inherent
viscosity, 3.7 gpd tenacity and 450 gpd modulus
Within the range of temperatures and exposure times of this invention,
basicity of up to about 10 meq of base per kg of yarn is acceptable.
Within that range, process operability and product properties are
acceptable. Above about 10 meq of base, the processability through the
heat treatment deteriorates badly and the polymer of the fibers is
believed to be severely degraded by that heat treatment through hydrolysis
and depolymerization reactions.
Very important to the operation of this invention, is the discovery that
increased inherent viscosities result from heat treatments at temperatures
of greater than 500.degree. C. of never-dried fibers having an acidity of
less than 60, and preferably less than 10, milliequivalents of acid per kg
of fiber and a basicity of less than 10, and preferably less than 2,
milliequivalents of base per kg of fiber.
Increased inherent viscosity indicates an increase in molecular weight of
the polymer which constitutes the fiber product. Fibers of polymer having
moderately increased molecular weight exhibit decreased solubility and,
also, exhibit increased resistance to deterioration due to moisture and
chemical exposure. Fibers of polymer having greatly increased molecular
weight, such as indicated by an inherent viscosity of 20, or greater,
exhibit complete insolubility. For most uses, the washing medium for
practice of this invention should be neutral or slightly basic.
The heat treatment of this invention can be carried out by various means.
One embodiment of this invention is in the use of a fluid jet which
conducts heated fluid, usually air, nitrogen, or steam, against the fibers
to be heat treated. The jet is a so-called forwarding jet which has a
fiber introduced at the back end of the jet and conducts the fiber through
the jet and out the front in a stream of heated fluid The jet provides
turbulent but subsonic movement of heated gas. FIG. 1 depicts a jet which
is effective for practice of this invention. The jet includes a fiber
introduction back part 1, a fluid introduction body part 2, and a heat
treating barrel extender 3. Fiber 4 is introduced into back part 1 at
fiber feed orifice 5, is conducted through that part to heat chamber 6,
and from there through barrel extender 3. Heated fluid is introduced into
heat chamber 6 by means of conduits 7 which may be present around heat
chamber 6 in any number of one or more and, if more than one,
substantially equally spaced.
The heated fluid and the fiber to be heat treated are conducted through
barrel extender 3 in the same direction, at the same or different speeds.
Some of the heated fluid also exits through the fiber feed orifice 5 in
the back part 1 so as to avoid entrainment of cool, outside, gases. The
speed of the heated fluid is carefully selected to provide high heat
transfer from the fluid through the jet device. For the purposes of this
invention, it has been concluded that a flow designated by a Reynolds
Number of greater than about 10,000 is preferred The Reynolds Number is
defined by the following equation:
##EQU1##
D=Jet diameter v=heated fluid velocity
.eta.=heated fluid density
.mu.=heated fluid viscosity
and all dimensions for those quantities are in consistent units
As an example of a determination of Reynolds Number for the practice of
this invention, there is taken the use of steam at 40 psig as the heated
fluid It is determined that steam under such pressure results in a flow of
2.0 SCFM (standard cubic feet per minute) at a temperature of about
550.degree. C. when the jet diameter (throat) is 0.18 centimeters The
effective steam velocity calculates to 2.8.times.10.sup.4 centimeters per
second Standard tables give the density of such steam as
9.7.times.10.sup.-4 : grams per cubic centimeter and the viscosity of such
steam as 3.0.times.10.sup.-4 poise. The Reynolds Number for this set of
conditions is 16,000:
##EQU2##
Use of the jet as a means for heating fibers permits heating convectively
at rates of approximately ten times the rate which is obtained using a
radiant oven.
The Reynolds Number or the degree of turbulence of gas in the jet has been
taken to be substantially independent of the yarn or fiber moving through
the jet. The rate of movement of the yarn or fiber through the jet is
important only to provide the desired or required heating time As a matter
of fact, the turbulent flow of the heated gas can be countercurrent to the
movement of the yarn or fiber being heat treated.
Another embodiment of this invention is in the use of an oven which is
fitted with a radient heat source and which provides drying and heat
treating energy Without the high relative velocity of fibers and heating
fluid which is associated with the jet, previously-described. The oven of
this embodiment is usually in the form of a tube or rectangular cavity
with dimensions much greater than the fiber to be heat treated. Heated
fluid is introduced into the oven at a rate such that there is very little
turbulence and the heating forces are primarily radiant in nature. FIG. 2
depicts an oven which is effective for practice of this invention. The
oven includes a tube 10 with fiber introduction end 11 and fiber exit end
12. Tube 10 is contained in insulating jacket 13 and there is provision
for introducing heated fluid into tube 10 by means of conduits 14 which
may be present around tube 10 in any number of one or more and, if more
than one, substantially equally spaced
Fiber 15 to be heat treated, is conducted through the oven at a speed
adequate to permit drying the fiber and exposing the dried fiber to the
proper heat energy. The heating fluid is supplied at a rate which is
adequate to maintain a desired temperature in the oven and carry
evaporated swelling medium away.
The two above-described embodiments for practice of this invention differ,
among other ways, in that the jet embodiment utilizes turbulent heated
fluid flow with a resultant, very thin boundary layer and very high,
substantially convective, heat transfer; the oven embodiment utilizes
relatively slow moving, laminar, heated fluid flow with a resultant
relatively thick boundary layer and low, substantially radiant, heat
transfer.
Due to the different mechanisms of heat transfer in the embodiments of this
invention, different results can be expected as a function of the time at
which a fiber is heated and the temperature at which the heating takes
place As was previously noted, use of the jet embodiment in practice of
this invention permits manufacture of fibers having a high Crystallinity
Index and use of the oven embodiment permits manufacture of fibers having
a high inherent viscosity. It is believed that increasing crystallinity is
developed in a fiber by increasing the temperature of the fiber heat
treatment and that crystallinity is developed very quickly and is, in
fact, developed so quickly that the degree of crystallinity is,
practically, a matter of the maximum temperature to which the fiber has
been exposed.
It is, also, believed that the reactions leading to increased inherent
viscosity are relatively slow processes compared with the rate of
crystallization, as discussed above. When fibers are exposed to high
temperatures for a time appreciably longer than that required for the
increase in crystallization, the reactions leading to increased inherent
viscosity will commence. When the rate of heating is relatively slow,
branching and crosslinking reactions will compete with the crystallization
reaction and limit, to some extent, the ultimate degree of crystallinity
which can be obtained.
In view of the above, it can be understood that practice of the jet
embodiment, with its rapid heat transfer and high rate of heating, yields
heat treated fibers with substantially increased crystallinity and an
inherent viscosity which has been increased only slightly. It can,
further, be understood that practice of the oven embodiment, with its
relatively slow heat transfer and slow rate of heating, yields heat
treated fibers with dramatically increased inherent viscosity and a
crystallinity which has been increased to a lesser degree.
The description of this invention is directed toward the use of fibers
which have been newly-spun and never dried to less than 20 percent
moisture prior to operation of the heat treating process. -t is believed
that previously-dried fibers cannot successfully be heat treated by this
process because the heat treatment is effective when performed on the
polymer molecules at the time that they are being dried and ordered into a
compact fiber structure.
The following test procedures represent descriptions of methods used to
evaluate the fibers prepared, in the Examples, as exemplifying the instant
invention.
TEST PROCEDURES
Inherent Viscosity
Inherent Viscosity (IV) is defined by the equation:
IV=1n(.eta.rel)/c
where c is the concentration (0.5 gram of polymer in 100 ml of solvent) of
the polymer solution and .eta.rel (relative viscosity) is the ratio
between the flow times of the polymer solution and the solvent as measured
at 30.degree. C. in a capillary viscometer. The inherent viscosity values
reported and specified herein are determined using concentrated sulfuric
acid (96% H.sub.2 SO.sub.4). Inherent viscosities reported as 20 dl/g or
greater are indications that the polymer being tested is insoluble. Fibers
of this invention can be insoluble.
Tensile Properties
Yarns tested for tensile properties are, first, conditioned and, then,
twisted to a twist multiplier of 1.1. The twist multiplier (TM) of a yarn
is defined as:
##EQU3##
The yarns tested in Examples 1-16 and 25-33 were conditioned at 25.degree.
C., 55% relative humidity for a minimum of 14 hours and the tensile tests
were conducted at those conditions. The yarns tested in Examples 17-24
were conditioned at 21.degree. C., 65% relative humidity for 48 hours and
the tensile tests were conducted at those conditions.
Tenacity (breaking tenacity), elongation (breaking elongation), and modulus
are determined by breaking test yarns on an Instron tester (Instron
Engineering Corp., Canton, Mass.).
Tenacity and elongation are determined in accordance with ASTM D2101-1985
using sample yarn lengths of 25.4 cm and a rate of 50% strain/min.
The modulus for a yarn from Examples 1-16 and 25-33 was calculated from the
slope of the secant at 0 and 1% strains on the stress-strain curve and is
equal to the stress in grams at 1% strain (absolute) times 100, divided by
the test yarn denier.
The modulus for a yarn from Examples 17-24 was calculated from the slope of
a line running between the points where the stress-strain curve intersects
the lines, parallel to the strain axis, which represent 22 and 27% of full
load to break (Full scale to break for 400 denier yarns was 20 pounds and
for 1200 denier yarns was 100 pounds). Results from tests of the two
methods for determining modulus are believed to be substantially
equivalent. For purposes of determining yarn moduli in claim conformance,
the method of Examples 1-16 and 25-33 will be used.
Denier
The denier of a yarn is determined by weighing a known length of the yarn.
Denier is defined as the weight, in grams, of 9000 meters of the yarn.
In actual practice, the measured denier of a yarn sample, test conditions
and sample identification are fed into a computer before the start of a
test; the computer records the load-elongation curve of the yarn as it is
broken and then calculates the properties.
Yarn Moisture
The amount of moisture included in a test yarn is determined by drying a
weighed amount of wet yarn at 160.degree. C. for 1 hour and then dividing
the weight of the water removed by the weight of the dry yarn and
multiplying by 100.
Acidity and Basicity of Yarn
Residual acid or base in a yarn sample was determined by boiling a weighed,
wet, yarn sample (about 20 grams) for one hour in about 200 ml deionized
water and about 15 ml 0.1 N sodium hydroxide, and then titrating the
solution to neutrality (pH 7.0) with standardized aqueous HCl. The dry
weight basis of the yarn sample was determined after rinsing the yarn
several times with water and oven drying. The acidity or basicity was
calculated as milliequivalents of acid or base per kilogram of dry yarn.
The amount of sodium hydroxide added to the solution must be such that the
pH of the system remains at pH 11.0 to 11.5 throughout the boiling step of
the test.
Moisture Regain
The moisture regain of a yarn is the amount of moisture absorbed in a
period of 24 hours at 70.degree. F. and 65% relative humidity, expressed
as a percentage of the dry weight of the fiber. Dry weight of the fiber is
determined after heating the fiber at 105.degree.-110.degree. C. for at
least two hours and cooling it in a dessicator.
Apparent Crystallite Size and Crystallinity Index
Apparent Crystallite Size and Crystallinity Index for poly-p-phenylene
terephthalamide fibers are derived from X-ray diffractograms of the fiber
materials. Apparent Crystallite size is calculated from measurements of
the half-height peak width of the diffraction peak at about 23.degree.
(2.THETA.), corrected only for instrumental broadening. All other
broadening effects are assumed to be a result of crystallite size.
The diffraction pattern of poly-p-phenylene terephthalamide is
characterized by the X-ray peaks occurring at about 20 and 23.degree.
(2.THETA.). As crystallinity increases, the relative overlap of these
peaks decreases as the intensity of the crystalline peaks increases. The
Crystallinity Index of poly-p-phenylene terephthalamide is defined as the
ratio of the difference between the intensity values of the peak at about
23.degree. and the minimum of the valley at about 22.degree. to the peak
intensity at about 23.degree., expressed as percent. It is an empirical
value and must not be interpreted as percent crystallinity.
X-ray diffraction patterns of yarn samples are obtained with an X-ray
diffractometer (Philips Electronic Instruments; ct. no. PW1075/00) in
reflection mode. Intensity data are measured with a rate meter and
recorded either on a strip-chart or by a computerized data
collection-reduction system. The diffraction patterns were obtained using
the instrumental settings
Scanning Speed 1, 20 per minute;
Time Constant 2;
Scan Range 6.degree. to 38.degree., 2.THETA.; and
Pulse Height Analyzer, "Differential".
For the 23.degree. peak, the position of the half-maximum peak height is
calculated and the 2.THETA. value for this intensity measured on the high
angle side. The difference between this 2.THETA. value and the value at
maximum peak height is multiplied by two to give the peak breadth at half
height and is converted to degrees (1 in=4.degree.). The peak breadth is
converted to Apparent Crystal Size through the use of tables relating the
two parameters.
The Crystallinity Index is calculated from the following formula:
##EQU4##
A=Peak at about 23.degree., C=Minimum of valley at about 22.degree., and
D=Baseline at about 23.degree..
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preparation of poly-p-phenylene terephthalamide polymer.
Poly-p-phenylene terephthalamide polymer was prepared by dissolving 1,728
parts of p-phenylenediamine (PPD) in a mixture of 27,166 parts of
N-methylpyrrolidone (NMP) and 2,478 parts of calcium chloride cooling to
about 15.degree. C. in a polymer kettle blanketed with nitrogen and then
adding 3,243 parts of molten terephthaloyl chloride (TCl) with rapid
stirring. The solution gelled in 3 to 4 minutes. The stirring was
continued for 1.5 hours with cooling to keep the temperature below
25.degree. C. The reaction mass formed a crumb-like product. The
crumb-like product was ground into small particles which were then
slurried with: a 23% NaOH solution; a wash liquor made up of 3 parts water
and one part NMP; and, finally, water.
The slurry was then rinsed a final time with water and the washed polymer
product was dewatered and dried at 100.degree. C. in dry air. The dry
polymer product had an inherent viscosity (IV) of 6.3, and contained less
than 0.6% NMP, less than 440 PPM Ca++, less than 550 PPM Cl--, and less
than 1% water.
Spinning and heat treating of fibers are extremely complicated processes.
Evaluation of fibers with duplication of test results is often difficult.
In the examples of the invention which follow, there are a few yarns with
test results outside of limits set for the physical properties of yarns at
the edge of the present invention. Such test results outside of the limits
set for the invention are few and are generally no farther outside the
limits than the expected experimental error.
EXAMPLE 1
This Example describes the preparation of a series of yarns from
poly-p-phenylene terephthalamide like that above-prepared which yarns
differ from each other primarily in denier and moisture content
An anisotropic spinning solution was prepared by dissolving the polymer in
100.1% sulfuric acid so as to produce a 19.3 wt percent solution. The
spinning solution was extruded through a spinneret at about 74.degree. C.
into a 4 mm air gap followed by a coagulating bath of 10% aqueous sulfuric
acid maintained at a temperature of 3.degree. C. in which overflowing bath
liquid passed downwardly through an orifice along with the filaments. The
spinneret had 134 to 1000 spinning holes (depending on the denier) of
0.064 millimeter diameter. The filaments were in contact with the
coagulating bath liquid for about 0.025 seconds. The filaments were
separated from the coagulating liquid, forwarded at various speeds
(300-475 ypm) depending on the yarn denier desired and washed in two
stages In the first stage, water having a temperature of 15.degree. C. was
sprayed on the yarns to remove most of the acid. In the second stage, an
aqueous solution of sodium hydroxide was sprayed on the yarns followed by
a spray of water. In the second stage, the temperature of the liquid
sprays was 15.degree. C. Residual acid or base in the yarns was determined
as milliequivalents per kg of yarn. The exterior of the yarns was stripped
of excess water and yarns were either wound up without drying (yarn
moisture of about 85%) or they were partially dried on a steam-heated roll
to as low as 35 weight percent yarn moisture based on dried fiber
material. The polymer in the yarns so prepared had an inherent viscosity
of 5.4 to 5.6. Properties of the series of yarns so produced are given in
Table 1. The yarns of this Example, A-G, differed from each other
in denier, yarn moisture, and acidity or basicity.
TABLE 1
__________________________________________________________________________
Acidity(A)
Forward- or
ing Yarn Basicity(B)
Speed Moisture
Inh.
Ten.
Modulus
(meq./kg.
Item
(ypm)
Denier
(%) Vis.
(gpd)
(gpd)
of yarn)
__________________________________________________________________________
A 450 2130
85 5.5 24.3
513 6.30 (A)
B 450 2130
50 5.5 24.4
523 8.65 (A)
C 300 1140
85 5.5 26.2
545 5.50 (A)
D 300 1140
35 5.6 26.7
532 1.46 (B)
E 475 400
85 5.5 26.5
553 8.50 (A)
F 400 200
85 5.4 22.6
554 --
G 1140
85 5.5 24.6
436 --
__________________________________________________________________________
EXAMPLES 2-11
These Examples describe the preparation of a series of high modulus, high
tenacity, and high inherent viscosity poly-p-phenylene terephthalamide
yarns by heat-treating the yarns of Example 1 (items A-F) in an oven.
Each of the wet yarns of Example 1 was tensioned and heat-treated in a 40
ft oven for a given time, temperature and tension. Yarn speeds were in the
range of 75-200 ypm and were selected to give the desired residence times
The oven was electrically heated and heated the yarns primarily by radiant
heat and, only partially, by convective heat. The oven was continuously
purged with nitrogen preheated to oven temperature, which, combined with
steam from the drying yarn, created a nitrogen/steam atmosphere. The yarn
leaving the oven was advanced by a set of water-cooled rolls during which
the yarn temperature was reduced to about 25.degree. C. The oven treating
conditions for Examples 2-11 are given in Table 2, while the properties of
the heat treated yarns are given in Table 3.
TABLE 2
______________________________________
HEAT TREATING CONDITIONS
Feed Yarn
Example 1,
Oven Temp. Heating Time
Tension
Example
Item (.degree.C.)
(Sec.) (gpd)
______________________________________
2 A 660 8.0 3.0
3 B 640 10.7 3.0
4 C 600 6.7 2.0
5 C 625 6.7 2.0
6 D 550 8.9 2.0
7 D 600 8.9 2.0
8 D 640 6.7 2.0
9 E 550 4.0 2.2
10 E 600 6.0 2.2
11 F 540 5.0 1.8
______________________________________
TABLE 3
__________________________________________________________________________
HEAT-TREATED YARN PROPERTIES
Denier Elong. Mois-
of at Crystal-
ture
Exam-
Treated
Tenacity
Modulus
Break
Inh. Vis.
inity Regain
ple Yarn (gpd)
(gpd)
(%) (dl/g)
Index (%)
(%)
__________________________________________________________________________
2 2110 18.7 1142 1.5 >20.0
72 --
3 2087 18.6 1136 1.6 13.9 72 --
4 1112 21.0 1101 1.8 7.0 72 1.2
5 1100 19.6 1193 1.6 8.8 73 1.0
6 1130 21.9 1061 1.9 7.0 70 --
7 1124 19.7 1166 1.6 15.0 72 --
8 1117 18.8 1244 1.5 >20.0
74 --
9 369 22.4 1094 1.9 6.4 73 --
10 371 19.1 1261 1.5 14.2 74 0.9
11 188 19.9 1102 1.7 6.3 72 --
__________________________________________________________________________
These examples indicate that the poly-p-phenylene terephthalamide yarns of
this invention with moduli greater than about 1100 gpd, inherent
viscosities greater than about 6.5, tenacities greater than -8 gpd, and
crystallinity indices at least 70%, were prepared using the following oven
heating conditions: oven temperature greater than 500.degree. C.
(preferably 550.degree.-660.degree. C.), heating times 4-11 sec., and
tension 1.5-3.0 gpd. Note that the polymers of Examples 2 and 8 are
insoluble.
EXAMPLE 12
A 380 denier, poly-p-phenylene terephthalamide yarn with 85% yarn moisture
(feed yarn, Example 1E, Table 1) was heat-treated in an oven at
640.degree. C.: for 5.75 seconds by the same general procedure of Examples
2-11, except that the tension, during heating, was only 0.75 gpd. The yarn
so produced exhibited a tenacity of 15.8 gpd and a modulus of 1045 gpd. At
a tension of about 2 gpd, the modulus of the yarn of this Example 12 would
have been expected to be greater than 1250 gpd and the tenacity greater
than 18 gpd for the time and temperature utilized (see Example -0 in
Tables 2 & 3 for comparison). cl EXAMPLES 13-16
These Examples describe the oven heat-treatment of 400 and 1140 denier
polY-p-phenYlene terephthalamide yarns at less than the preferred
temperatures.
Feed yarns (Example 1, Items C, D & E) were heat-treated in an oven by the
same general manner as in Examples 2-11, except that the temperatures were
450.degree.-500.degree. C. Specific heating conditions for each Example,
13 through 16, are listed in Table 4. Heat-treated yarn properties are
given in Table 5. None of the yarns of these examples exhibit the
combination of modulus/inherent viscosity/tenacity/crystallinity index
which represent the yarns of this invention; that is, both the moduli and
inherent viscosities fall below the desired range.
TABLE 4
__________________________________________________________________________
Feed Yarn Heating
Example 1
Yarn Oven Temp.
Time Tension
Example
Item Moisture (%)
(.degree.C.)
(Sec.)
(gpd)
__________________________________________________________________________
13 E 85 450 6.0 2.2
14 E 85 500 6.0 2.2
15 C 85 500 8.9 2.0
16 D 35 500 8.9 2.0
__________________________________________________________________________
TABLE 5
__________________________________________________________________________
Mois-
ture
Exam- Tenacity
Modulus
Elong. at
Inh. Vis.
C.I.
Regain
ple Denier
(gpd)
(gpd)
Break (%)
(dl/g)
(%) (%)
__________________________________________________________________________
13 370
23.4 1058 2.1 5.2 70 1.2
14 373
22.5 103 2.0 5.4 70 1.5
15 1119
23.2 986 2.2 5.5 70 --
16 1141
23.0 1005 2.2 5.7 68 --
__________________________________________________________________________
EXAMPLES 17-22
These Examples describe the preparation of a series of high modulus, high
tenacity and highly crystalline poly-p-phenylene terephthalamide yarns by
heat-treating never-dried feed yarns under tension in a forwarding jet
For each of these Examples, yarn from Example 1, Item E for all Examples
except 18 and Item G for Example 18, above, was immersed in water. An end
from the immersed yarn was passed through a tension gate and onto a feed
roll. The resulting yarn moisture was about 100%. From the feed roll, the
yarn was passed through a forwarding jet of the type shown in FIG. 1 with
a barrel extender which made the overall length of the jet eight inches.
In the jet, the yarn was dried and heat-treated with superheated steam or
heated air, depending on the specific Example. From the jet, the yarn was
passed over a draw roll so as to maintain tension on the yarn (between 2
and 4 gpd depending on the Example) in the heat-treating zone, and thence
to a wind-up roll. Water was applied to the yarn just after the jet to
reduce static bloom. Table 6 contains the specific feed yarn and jet
conditions used for each Example, while Table 7 provides the properties of
the heat-treated yarns so produced.
The yarns of Examples 17-22 exhibit a combination of high modulus (greater
than 1100 gpd), high tenacity (greater than 18 gpd) and high crystallinity
(crystallinity index, at least 76%), and Apparent Crystal Size, at least
74.ANG.).
EXAMPLES 23-24
These two examples describe the preparation of poly-p-phenylene
terephthalamide yarns by the jet heat-treating procedures described in
Examples 17-22, except that the exposure times at 500.degree. C. were too
long and too short, respectively, to give yarns with the desired
combination of properties. Processing conditions are given in Table 6 and
yarn properties in Table 7. At the short heating time of 0.5 sec. at
500.degree. C. for Example 25, both the modulus (1053 gpd) and
crystallinity properties (Crystallinity Index, 72%; Apparent Crystal Size,
71.ANG.) of the yarn were outside of the desired range. At the long
heating time of 2.5 sec. at 500.degree. C., the yarn tenacity (16.7 gpd)
fell below the desired range.
TABLE 6
__________________________________________________________________________
Mois-
ture Resi-
on Yarn Gas Flow Ten-
dence
Rey-
Exam-
Yarn
Speed
Gas Press.
Temp.
Rate sion
Time
nolds
ple (%) (m/m)
Atm.
(psig)
(.degree.C.)
(SCFM)
(gpd)
(sec)
(.times. 1000)
__________________________________________________________________________
17 100 17 air 40 550 1.9 4.0 0.7 22
18 100 17 steam
80 600 2.7 3.8 0.7 26
19 100 25 steam
40 600 1.8 2.0 0.5 14
20 100 50 steam
40 600 1.8 2.2 0.25
14
21 100 15 steam
40 500 2.0 2.0 0.8 18
22 100 10 steam
40 500 2.0 2.0 1.3 18
23 100 5 steam
40 500 2.0 2.0 2.5 18
24 100 25 steam
40 500 2.0 2.0 0.5 18
__________________________________________________________________________
TABLE 7
__________________________________________________________________________
Appar.
Mois-
Ten-
Break
Modu-
Crystal.
Crystal.
ture
Inherent
Exam- acity
Elong.
lus Index
Size Regain
Viscos.
ple Denier
(gpd)
(%) (gpd)
(%) (.ANG.)
(%) (dl/g)
__________________________________________________________________________
17 377 18.6
1.5 1141
79 78 1.2 5.7
18 1165
19.7
1.5 1304
76 74 1.0 5.5
19 375 20.2
1.5 1278
76 77 1.1 6.7
20 363 19.1
1.4 1268
77 78 1.1 5.4
21 376 18.1
1.5 1125
76 74 1.4 5.8
22 377 18.3
1.5 1145
77 76 1.4 6.0
23 372 16.7
1.4 1183
77 77 1.2 6.0
24 370 19.0
1.7 1053
72 71 2.4 5.0
__________________________________________________________________________
EXAMPLES 25-33 AND COMPARISON EXAMPLES C1-C7
Examples 25-33 and Comparison Examples C1-C7 describe the preparation of a
series of poly-p-phenylene terephthalamide yarns using rinsing and washing
processes which result in varying levels of acidity and basicity.
A series of nominally 400 denier (267 filaments per yarn) poly-p-phenylene
terephthalamide yarns was prepared as described in Example 1 except that
the second stage of washing for yarns in this series was varied from water
sprays to sprays of caustic solution with increasing concentration of
sodium hydroxide ranging from 0.1 to 1 8%, followed by sprays of water or
caustic solution with concentrations ranging from 0.01 to 0.5%. Residual
acid or base in the yarns ranged from as high as 136 meq of acid per kg of
yarn, through essentially neutral yarns, to as high as 106 meq of base per
kg of yarn. The exterior of the yarns was stripped of excess water and the
yarns were wound up without drying (yarn moisture of about 85%)
The yarns prepared as above were tensioned and heat-treated in an oven (17
in long) at 600.degree. C. for 5.7 sec at a tension of 2.0-2.5 gpd. The
properties of the yarn before and after heat treatment are given in Table
8.
It can be seen from Table 8 that yarns having acidity levels up to acidity
of about 60 (Examples 25-30) gave acceptable processability during oven
heating, high modulus, good strength retention and high inherent
viscosity. Above acidity of about 60, yarn processability deteriorated
abruptly, such that the yarn broke under processing tensions and could not
be strung up (Comparison Examples C1-C3).
On the basic side, spun yarns with basicity up to about 10 could be
successfully processed, and the properties of the resulting oven-treated
yarns were acceptable (Examples 31-33). At basicity of greater than about
10, yarn properties and processability deteriorated (Comparison Examples
C4-C7).
TABLE 8
__________________________________________________________________________
Before Heating
Acidity Opera- After Heating
or basi-
Inher.
bility Strgth
Inher.
Exam- city Viscos.
during Mod.
Reten.
Viscos.
ple (Meq/kg)
(dl/g)
heating
(gpd)
(%) (dl/g)
__________________________________________________________________________
C1 136 Acid
5.4 Oven breaks
-- -- --
Can't
string up
C2 123 Acid
5.2 Oven breaks
-- -- --
Can't
string up
C3 65 Acid
5.6 Oven breaks
-- -- --
Can't
string up
25 54 Acid
5.7 Acceptable
1160
73 >20
26 42 Acid
5.6 Acceptable
1180
68 17.0
27 24 Acid
5.2 Acceptable
1150
64 16.5
28 21 Acid
5.9 Acceptable
1170
66 9.5
29 7 Acid
5.7 Acceptable
1180
58 10.5
30 4 Acid
5.1 Acceptable
1151
60 8.5
31 2 base
5.3 Acceptable
1064
54 8.8
32 4 base
5.6 Acceptable
1140
58 8.7
33 8 base
5.7 Acceptable
1084
50 8.2
C4 14 base
4.5 Oven breaks
-- -- --
Can't
string up
C5 23 base
5.4 Poor 1103
48 7.0
process
continuity
C6 63 base
4.8 Poor 1061
50 4.3
process
continuity
C7 106 base
5.8 Oven breaks
-- -- --
Can't
string up
__________________________________________________________________________
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